The output transistors can be BC548 and BC558. The circuit is from a 1975 documentation showing a frequency response from 90 Hz to 12.5 kHz.
This circuit was originally developed in 1989 to allow the triggering of loads from audio signals...
A circuit in which the light turns on smoothly and goes out quickly, but which can be adjusted more...
Found in old documentation, this circuit is intended for low level amplitude modulation with low...